Heretofore, among ozone generating apparatuses used in a water treatment and the like, many of them have utilized silent discharge. A basic configuration of the ozone generating apparatuses that utilize silent discharge, comprises such a structure in which a cylindrical dielectric tube with a metal film formed on the inner surface thereof, is inserted in a cylindrical metal tube so that a predetermined gap is given between the inner wall of the metal tube and the outer wall of the dielectric tube. By flowing an oxygen-containing source gas (air, oxygen gas, etc.) in the gap, and by applying a high-voltage AC voltage between the metal tube and the metal film on the inner surface of the dielectric tube to thereby generate an AC field in the gap through the dielectric material of the dielectric tube, the source gas is discharged and oxygen in the source gas is ozonized, so that ozone is produced.
Recently, for such an ozone generating apparatus used in a treatment of huge volume of water, because of increasing treatment volume, it is required to enhance its treatment capacity without size increase. In order to fulfill such a requirement, it is necessary to increase an amount of ozone produced per unit size of the apparatus, and for that reason, it is necessary to increase a discharge power density. However, with the increase in the discharge power density, heat-related problems are also increased. In particular, there is a problem that cooling unevenness emerges near an end portion of the metal tube. In order to suppress this, such a measure has been taken that a discharge suppressing member is provided in a portion of the gap at the end portion (for example, Patent Document 1).
Heat generated by the discharge is taken away by cooling water that circulates outside the metal tube, so as to inhibit the dielectric tube from becoming too high temperature. If the dielectric tube becomes too high temperature, since its breakdown voltage decreases, it no longer withstand the applied high voltage and will be dielectrically broken down, resulting in damage of the apparatus. Meanwhile, in a case of no discharge suppressing member, because the discharge occurs space between the dielectric tube and the metal tube whereas no cooling water circulates in a tube sheet portion, a temperature near the tube sheet portion becomes highest, so that a temperature of the dielectric tube in contact therewith becomes highest at a portion facing to the tube sheet portion. Feedable power to the apparatus is determined so that the highest temperature of the dielectric tube equal to or less than a reference temperature. Thus, if the temperature of the dielectric tube at the portion facing to the tube sheet portion can be decreased, feedable power becomes larger, so that an amount of ozone produced by the apparatus can be increased. Accordingly, when the discharge suppressing member is placed at the tube sheet portion to thereby suppress the discharge thereat, such an effect vided that the temperature of this portion is decreased, so that the average power can be made larger to thereby increase the amount of ozone produced by the apparatus.